Deterioration signal generation device for oxygen sensor

ABSTRACT

A deterioration signal generation device for an oxygen sensor having a power supply different than a power supply connected to an external device, including a connection unit for electrically connecting the ground lines of the respective power supplies; a first acquisition unit for electrically connecting to a first output line at a reference potential side and to a second output line at a sensor potential side of the oxygen sensor, to obtain first and second potentials, respectively; an operation unit that calculates a first differential value between the first and second potentials; a processing unit that performs an operation on the first differential value; a second acquisition unit that acquires a third potential of a first input line at a reference potential side of the external device; and an output unit that generates the deterioration signal by superposing the second differential value on the third potential.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/009,261 filed Jan. 19, 2011, which claims benefit to JapanesePatent Application No. 2010-010429 filed Jan. 20, 2010. The above-notedapplications are incorporated herein by reference to their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a deterioration signal generationdevice for an oxygen sensor which generates, from a detection signal ofan oxygen sensor, a pseudo output value (degeneration output signal)simulating a deteriorated sate of the oxygen sensor, the oxygen sensoroutputting a detection signal based on the concentration of oxygen inexhaust gas of an internal combustion engine.

2. Description of the Related Art

A related art oxygen sensor is known which is mounted in an exhaustpassage of an internal combustion engine, such as a vehicle engine, tocheck whether the air-fuel ratio is rich or lean based on theconcentration of oxygen in the exhaust gas. A detection signal outputfrom the oxygen sensor is transmitted to an ECU (Electronic ControlUnit) performing various engine controls, and the ECU executes feedbackcontrol of the air-fuel ratio such as by adjusting the fuel injectionamount in the engine based on the detection signal thus received.

Since such oxygen sensors may slightly deteriorate due to aging upon useand exposure to exhaust gas in an exhaust gas passage over a long periodof time, programs or devices are incorporated into the ECU for detectingdeterioration of the oxygen sensor. While an actual vehicle is tested tocheck the operation of a program, etc., for detecting deterioration ofthe oxygen sensor, deterioration signal generation devices(deterioration simulators) capable of generating a pseudo deteriorationsignal simulating a deteriorated state of the oxygen sensor have beendeveloped (see for example, Patent Document 1). For example, thedeterioration signal generation device of Patent Document 1 is disposedbetween a normal oxygen sensor (reference sensor) mounted on a targetvehicle to be tested and an ECU. The device processes a detection signalinput from the reference sensor to generate a pseudo deteriorationsignal and outputs the deterioration signal to the ECU.

[Patent Document 1] JP-A 2004-93957

3. Problems to be Solved by the Invention

Since an ECU, however, is designed according to different standards forindividual manufacturers, or vehicle models, reference potentials as areference of the operational potential of the ECU itself may vary. Sincea reference potential of an oxygen sensor connected to the ECU issubject to a reference potential of the ECU, a detection signal outputfrom the oxygen sensor to the ECU is also subject to the referencepotential of the ECU. Accordingly, increased testing accuracy has beenrequired for each of deterioration signal generation devices outputtingan appropriate signal level based on a reference potential of the ECU ofindividual manufacturers, or vehicle models.

In addition, the ECU is generally supplied with electric power from avehicle battery, but arrangement of the battery and ECU of the vehicleis fixed and the wiring resistance in an electric power supply line mayeasily increase. In contrast, the deterioration signal generation deviceis readily arranged such that the wiring resistance in the electricpower supply line may be relatively low as compared with that of theECU, even though electric power is supplied from a battery or anexternal power supply. The reference potential of the deteriorationsignal generation device is adjusted to equal the reference potential ofthe ECU. However, for example, although each of the reference potentialsis connected to ground, it is difficult to make each of the referencepotentials exactly equal whenever the test is performed due to an effectsuch as wiring resistance.

SUMMARY OF THE INVENTION

The invention has been made to solve the above problems. It is thereforean object of the invention to provide a deterioration signal generationdevice for an oxygen sensor capable of generating a deterioration signalby acquiring a detection signal with high accuracy, and withoutdepending on operational circumstances upon connecting an externalapparatus and establishing a common ground.

According to a first aspect, the present invention provides adeterioration signal generation device for generating a deteriorationsignal simulating a deteriorated state of an oxygen sensor from adetection signal of the oxygen sensor, the oxygen sensor outputting adetection signal which abruptly changes in signal value around aspecific air-fuel ratio in response to the concentration of oxygen in anexhaust gas of an internal combustion engine, the deterioration signalgeneration device outputting the deterioration signal to an externaldevice, and the deterioration signal generation device being suppliedwith electric power from a power supply different than a power supplyconnected to the external device, the deterioration signal generationdevice comprising: a connection unit for electrically connecting aground line of a first power supply supplying electric power to theexternal device and a ground line of a second power supply supplyingelectric power to the deterioration signal generation device; a firstacquisition unit for electrically connecting the deterioration signalgeneration device to a first output line at a reference potential sideof the oxygen sensor and to a second output line at a sensor potentialside of the oxygen sensor that changes in potential in response tooxygen concentration, and that acquires a first potential of the firstoutput line and a second potential of the second output line; anoperation unit that calculates a first differential value between thefirst potential and the second potential; a processing unit thatperforms one or more operations on the first differential value inresponse to a target deterioration state to thereby obtain a seconddifferential value; a second acquisition unit that acquires a thirdpotential of a first input line at a reference potential side of theexternal device, which first input line would be connected to the firstoutput line in a case where the oxygen sensor is connected to theexternal device; and an output unit that generates the deteriorationsignal having as a signal value a fourth potential obtained bysuperposing the second differential value on the third potential, tothereby output the deterioration signal to a second input line at asensor potential side of the external device, which second input linewould be connected to the second output line in a case where the oxygensensor is connected to the external device.

In the first aspect, even though each of an external apparatus and adeterioration signal generation device are connected to different powersupplies, a reference potential of an external apparatus and a referencepotential of a deterioration signal generation device may be made nearlyequal by electrically connecting the ground line of a first power supplyand the ground line of a second power supply. Accordingly, since a firstpotential as a potential reference of the reference sensor may bemaintained nearly equal in both the case where a reference sensor(oxygen sensor) is connected to an external apparatus and in the casewhere a reference sensor (oxygen sensor) is connected to a deteriorationsignal generation device, the value of a detection signal acquired bythe deterioration signal generation apparatus may originally be equal tothe value of a detection signal acquired by the external apparatus. Inaddition, since a first differential value is calculated and processedby acquiring a first potential and a second potential of the referencesensor, this process is independent of a reference potential.Accordingly, a process with a high degree of accuracy may be performedwithout affecting the first differential value even though the referencepotential of the deterioration signal generation device may change.Further, the deterioration signal has a high degree of accuracy withoutdepending on a reference potential of the deterioration signalgeneration device, by generating a deterioration signal having as asignal value a fourth potential which results from superposing thesecond differential value acquired by the process onto the thirdpotential obtained from the external apparatus. In addition, even thougha reference potential of the external apparatus is affected and changedby noise or offset due to a load connected to the first power supply,the third potential as a reference of the signal value of thedeterioration signal likewise changes. Accordingly, the differentialvalue between the third potential and the fourth potential, that is, asecond differential value, is not affected, and thus the degree ofaccuracy is high.

According to a second aspect, the present invention provides adeterioration signal generation device for generating a deteriorationsignal simulating a deteriorated state of an oxygen sensor from adetection signal of an oxygen sensor, the oxygen sensor outputting adetection signal which abruptly changes in signal value around aspecific air-fuel ratio in response to the concentration of oxygen in anexhaust gas of an internal combustion engine, and the deteriorationsignal generation device outputting the deterioration signal to anexternal device, the deteriorated signal generating device beingsupplied with electric power from a power supply commonly connected tothe external device, the deterioration signal generation devicecomprising: a first acquisition unit for electrically connecting thedeterioration signal generation device to a first output line at areference potential side of oxygen sensor and to a second output line ata sensor potential side of the oxygen sensor that changes in potentialin response to oxygen concentration, and that acquires a first potentialof the first output line and a second potential of the second outputline; an operation unit that calculates a first differential valuebetween the first potential and the second potential; a processing unitthat performs one or more operations on the first differential value inresponse to a target deterioration state to thereby process into asecond differential value; a second acquisition unit that acquires athird potential of a first input line at a reference potential side ofthe external device, which first input line would be connected to thefirst output line in a case where the oxygen sensor is connected to theexternal device; and an output unit that generates the deteriorationsignal having as a signal value a fourth potential obtained bysuperposing the second differential value on the third potential, tothereby output the deterioration signal to a second input line at asensor potential side of the external device, which second input linewould be connected to the second output line in a case where the oxygensensor is connected to the external device.

In the second aspect of the invention, an external apparatus and adeterioration signal generation device are connected to the same powersupply, such that a reference potential of the external apparatus and areference potential of the deterioration signal generation device becomenearly equal. Accordingly, since a first potential as a potentialreference of the reference sensor may be maintained in a nearly equalstate in both the case where a reference sensor (oxygen sensor) isconnected to an external apparatus and in the case where a referencesensor (oxygen sensor) is connected to a deterioration signal generationdevice, the signal value of a detection signal acquired by thedeterioration signal generation device may originally be equal to thesignal value of detection signal acquired by the external apparatus. Inaddition, since a first differential value is calculated and processedby acquiring a first potential and a second potential of the sensor,this process is independent of a reference potential. Accordingly, aprocess with a high degree of accuracy may be performed withoutaffecting the first differential value even though the referencepotential of the deterioration signal generation device may change.Further, the deterioration signal has a high degree of accuracy evenwithout depending on a reference potential of the deterioration signalgeneration device, by generating a deterioration signal having as asignal value a fourth potential which results from superposing thesecond differential acquired by the process onto the third potentialobtained from the external device. In addition, even though a referencepotential of the external apparatus is affected and changed by noise oroffset due to a load connected to the first power supply, the thirdpotential as a reference of the signal value of the deterioration signallikewise changes. Accordingly, the differential value between the thirdpotential and the fourth potential, that is, a second differentialvalue, is not affected, and thus the degree of accuracy is high.

In a preferred embodiment of the first or second aspects, the processingunit performs, according to a deterioration state (deterioration mode)of the oxygen sensor that a user using the deterioration signalgeneration device of the invention requires (intentionally sets), atleast one operation that simulates a predetermined deterioration stateselected from the group consisting of: a gain operation for changinggain of a signal value of the detection signal, an offset operation forchanging a signal value of the detection signal up or down by a fixedamount; a timing characteristics operation for delaying response of thedetection signal to a change in concentration of a specific component(e.g., oxygen) in a target gas to be measured, and a responsecharacteristics operation for changing a rate of change (time constantdelay) of the detection signal in response to a change in concentrationof a specific component in a target gas to be measured, to therebyprocess the first differential value into the second differential value.Since one or more of the gain operation, offset operation, timingcharacteristics operation and response characteristics operation areperformed, thereby simulating various deterioration states of the oxygensensor, various tests or developments may be performed more definitely,more accurately and more easily. In addition, various operations such asgain operation, etc., may separately produce deterioration signalsrepresenting states that are different from each other, in cases wherethe air-fuel ratio changes from a lean side to a rich side and from arich side to a lean side on the basis of a specific air-fuel ratio(e.g., theoretical fuel-air ratio) as a boundary.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative aspects of the invention will be described in detail withreference to the following figures wherein:

FIG. 1 is a block diagram showing a schematic configuration of a sensorsimulator according to the first illustrative embodiment of theinvention;

FIG. 2 is a view showing a schematic configuration of an electriccircuit of the output circuit 40;

FIG. 3 is a flow chart of a process program;

FIG. 4 is a view illustrating outlines of a gain process, an offsetprocess, a response delay process, and a lag time delay process; and

FIG. 5 is a block diagram showing a schematic configuration of thesensor simulator 1 according to a second illustrative embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in detail with reference to thedrawings. However, the present invention should not be construed asbeing limited thereto.

First Illustrative Embodiment

Hereinafter, a deterioration signal generation device for an oxygensensor according to a first illustrative embodiment of the inventionwill be described in brief. The oxygen sensor of the invention includes,for instance, an oxygen sensor (a so called λ type oxygen sensor)outputting a detection signal whose output value abruptly changes on thebasis of a specific air-fuel ratio (a theoretical fuel-air ratio in thefirst illustrative embodiment) as a boundary and in response to theconcentration of oxygen in an exhaust gas. The sensor simulator 1 isconnected to an oxygen sensor 3, which is in a normal state (notdeteriorated), and identical in configuration to the target oxygensensor of product for which a deteriorated state is simulated.

Meanwhile, a detailed illustration of the configuration of the oxygensensor is omitted because a conventional oxygen sensor can be used asthe oxygen sensor in the invention. Hereinafter, a detection principleof the air-fuel ratio (the concentration of oxygen in an exhaust gas) ofan exhaust gas by a sensor element employed in an oxygen sensor,however, will be described briefly. The sensor element has a cup shapeor a plate shape in which a solid electrolyte, which is made ofzirconium having oxygen-ion conductivity above an active temperature, issandwiched between a pair of porous electrodes. The oxygen sensor(sensor device) detects the concentration of oxygen based on theprinciple that oxygen ions move in the solid electrolyte to therebyproduce an electromotive force (detection signal) when there is adifference in oxygen partial pressure between the atmospheres contactingopposing sides (one side is formed with an exhaust gas atmosphere andthe other side is formed with a reference gas atmosphere) of the solidelectrolyte.

The signal value of the detection signal indicates a potentialdifference between the electrode of the one side (OZ(−) electrode) andthe electrode of the other side (OZ(+) electrode), based on thepotential of the one side porous electrode (OZ(−) electrode). The signalvalue sharply (abruptly) changes between the rich side and the lean sideat a point where the air-fuel ratio of exhaust gas corresponds to atheoretical air-fuel ratio. Generally, in the case where the air-fuelratio of exhaust gas is on the rich side (in the case where theconcentration of oxygen in an exhaust gas is lower than theconcentration of oxygen of a theoretical air-fuel ratio), the signalvalue (potential difference) of the detection signal representsapproximately 0.9 V. In the case of the lean side (the case where theconcentration of oxygen in an exhaust gas is greater than theconcentration of oxygen of a theoretical air-fuel ratio), the signalvalue represents approximately 0.05 V. As an example of such an oxygensensor, the embodiment of the invention may employ the oxygen sensordisclosed in JP Patent publication No. 2004-138599-A, incorporatedherein by reference. The oxygen sensor has a form in which a heater isinterposed within a cup-shaped sensor element, a front end of the sensorelement is surrounded by a protector having gas-flow holes, and thesensor element is held within a housing. The oxygen sensor has aconnector for connecting with an external apparatus (ECU 3 which will bedescribed below), and the connector is electrically connected to theOZ(−) electrode of sensor device and the OZ(+) of oxygen device througha lead line and a terminal electrode.

As shown in FIG. 1, the sensor simulator 1 is arranged between areference sensor 2 as an oxygen sensor which is mounted in an exhaustpassage (not shown) of a vehicle and an electronic control unit (ECU) 3for electronically controlling a vehicle. The sensor simulator 1includes a receptacle connected to a connector of the reference sensor 2and a connector connected to the ECU 3 instead of the reference sensor2. The reference sensor 2 outputs a detection signal in response to theconcentration of oxygen in an exhaust gas flowing within the exhaustpassage, and the detection signal is input to the sensor simulator 1.The sensor simulator 1 processes the signal value of the inputteddetection signal by performing a processing program, described below, ina microcomputer 10, generates a deterioration signal through an outputcircuit, described below, and outputs it to the ECU 3. The ECU 3controls an engine which is not shown (for example, injection timingcontrol, or control of an injection amount of fuel being injected froman injector, or ignition timing control), in response to the inputteddeterioration signal. In addition, the ECU 3 supplies a heater drivingvoltage to a heater circuit (not shown) of the reference sensor 2, andinstructs the earlier activation of a sensor element (not shown), or thestabilization of a sensor device even after activation.

The sensor simulator 1 includes a microcomputer 10 having a CPU 11controlling itself, an EEPROM 12 being stored with processing programs,etc., and which is rewritable, and a RAM 13 temporarily storing variouskinds of data, within a casing not shown. Meanwhile, the CPU 11, EEPROM12 and RAM 13 of the microcomputer 10 are formed with a conventionalconfiguration.

The microcomputer 10 is connected to an input interface 20 through anA/D converter 30. The analog detection signal, which is input from thereference sensor 2 through the input interface 20, is converted to adigital signal by the A/D converter 30, and input to the microcomputer10. In more detail, the reference sensor 2 has a connector formed withan OZ(−) port and an OZ(+) port for acquiring the potential of theOZ(−)and OZ(+) electrodes of the sensor element. The OZ(−)and OZ(+)ports of the reference sensor 2 are connected to an IN 2 port and an IN1 port of the input interface 20 of the sensor simulator 1,respectively. Meanwhile, the input interface 20 corresponds to a “firstacquisition unit” of the invention. In addition, the OZ(−) port andOZ(+) port correspond to a “first output line” and a “second outputline” of the invention, respectively.

In addition, the input interface 20 includes a CON port, and the CONport is connected to a reference potential GND_A of the sensor simulator1. The input interface 20 acquires a potential of the OZ(−) port and theOZ(+) port of the reference sensor 2, and outputs the same to the AIDconverter 30, respectively, relative to a reference potential GND_Aconnected through the CON port. The A/D converter 30 converts apotential of the OZ(−) port and the OZ(+) port from an analog to adigital quantity, and inputs to the microcomputer 10.

The microcomputer 10 is also connected to a D/A converter 50. The D/Aconverter 50 is connected to an output circuit 40. The D/A converter 50performs a digital to analog conversion. This is because the signalvalues of the detection signal processed in the microcomputer 10 areoutput to the output circuit 40 formed with an electric circuitconfigured to perform analog processing.

The output circuit 40 includes an analog circuit formed by thecombination of a plurality of operational amplifiers and resistanceelements. The detailed configuration of the output circuit 40 as anexample is shown in FIG. 2. As shown in FIG. 2, the output circuit 40includes, for instance, four operational amplifiers OP1, OP2, OP3 andOP4, and eight resistance elements R1, R2, R3, R4, R5, R6, R7 and R8.Among them, the operational amplifiers OP1, OP2 and OP3 and resistanceelements R1, R2, R3, R4, R5, R6 and R7 form an instrumentation amplifier41. Non-inverting input terminals of the operational amplifiers OP2, OP3are connected to input terminals 42, 43 of the instrumentationamplifier, respectively. Inverting input terminals of the operationalamplifiers OP2, OP3 are connected to output terminals of the samethrough the resistance elements R3, R6, respectively, and are alsoconnected to each of the inverting input terminals through theresistance element R7. An output terminal of the operational amplifierOP2 is connected to an inverting input terminal of the operationalamplifier OP1 through the resistance element R2, and is also connectedto an output terminal of the operational amplifier OP1 corresponding tothe output terminal 45 of the instrumentation amplifier 41 through theresistance element R1. Meanwhile, the output terminal of the operationalamplifier OP3 is connected to a non-inverting input terminal of theoperational amplifier OP1 through the resistance element R5, and is alsoconnected to an input terminal 44 of the instrumentation amplifier 41through the resistance element R4. The instrumentation amplifier 41corresponds to the “output unit” of the invention.

Additionally, each of the terminals of the instrumentation amplifier 41is connected to four input/output ports (IN port, COM port, OUT port,REF port) of the output circuit 40, respectively. In more detail, theinput terminal 42 and the input terminal 43 each are connected to theCOM port and IN port, and the output terminal 45 is connected to the OUTport. In addition, the input terminal 44 is connected to an outputterminal of the operational amplifier OP4, and is also connected to aninverting input terminal of the operational amplifier OP4 through theresistance element R8. A non-inverting input terminal of the operationalamplifier OP4 is connected to the REF port. As shown in FIG. 1, the COMport of the output circuit 40 is connected to the reference potentialGND_A of the sensor simulator 1, and the IN port is connected to themicrocomputer 10 through the D/A converter 50, as described above. TheOUT and REF ports of the output circuit 40 are connected to the IN1 portand IN2 port of the input interface 7 of the ECU 3, respectively.Meanwhile, the IN1 port and IN2 port of the input interface 7 correspondto the “first input line” and the “second input line” of the invention,respectively.

As described below, the output voltage value of the deterioration signalgenerated in the microcomputer 10 is based on the reference potentialGND_A of the sensor simulator 1 as a reference potential. As shown inFIG. 2, in the output circuit 40, the differential between the outputvoltage value of the deterioration signal input to the IN port by theoperational amplifiers OP2, OP3 and the reference potential GND_A inputto the COM port is input to the operational amplifier OP1. In addition,a potential of the IN1 port of the input interface 7 of the ECU 3 isinput to the operational amplifier OP1 from the REF port. Theoperational amplifier OP1 superposes a potential GND_B differencebetween the output voltage value of the deterioration signal and thereference potential GND_A onto the potential at the IN1 port of theinput interface 7 of the ECU 3, thereby outputting the difference as adeterioration signal from the OUT port to the IN2 port of the inputinterface 7. That is, the deterioration signal, as a reference signalbased on the reference potential GND_B, is input to the ECU 3 by theoutput circuit 40. Meanwhile, the operational amplifier OP4 correspondsto the “second acquisition unit” of the invention.

Next, as shown in FIG. 1, the microcomputer 10 is additionally connectedto an input unit 60 and a display controller 70. The input unit 60 isdesigned to allow a user of the simulator 1 to input set points, etc.(gain factor Gain, voltage value Offset, set point of lag time T, etc.)which are used in a processing program, to the same. The input unit 60is employed with, for instance, a push switch, or a rotary switch.Meanwhile, the set points as inputted are stored in the EEPROM 12, andthe previously inputted set points are maintained even though they arereused after electric power to the sensor simulator 1 is cut off. Thedisplay controller 70 serves to control the display of a display unit 80displaying the inputted set points so that a user may check them. Thedisplay unit 80 is employed with an LCD display, for instance.

Although not shown, the sensor simulator 1 is also provided with a powersupply circuit, etc., and a BAT terminal of the sensor simulator 1 isconnected to a line (shown as dotted line) at an output side of anexternal power supply 5, thereby being supplied with electric power fromthe external power supply 5. A ground wire of the external power supply5 is connected to the reference potential GND_A of the sensor simulator1 through the S_GND terminal.

The ECU 3 has the same input interface 7 as the input interface 20 ofthe sensor simulator 1. The input interface 7 has the IN1 port, IN2 portand CON port, and the IN1 port and IN2 port are connected to the REFport and OUT port of the output circuit 40, respectively, as describedabove. The CON port of the input interface 7 is connected to thereference potential GND_B of the ECU 3. The reference potential GND_B isconnected to the ground wire of a vehicle battery 4 through the E_GND ofthe ECU 3. Further, the BAT terminal of the ECU 3 is connected to anoutput line (shown as dotted line) of the battery 4, thereby receivingelectric power from the battery 4. Meanwhile, the ECU 3 corresponds tothe “external apparatus” of the invention, and the battery 4 correspondsto the “first power supply”.

The battery 4 supplies electric power to various devices (loads) inaddition to the ECU 3. The ECU 3 is affected by operation of the loads,thereby causing noise or offset of potential in some cases. In addition,the ground wire of the battery 4, which is connected to the referencepotential GND_B of the ECU 3, is connected to connection point P2 on theground wire of the external power supply 5, which is connected to thereference potential GND_A of the sensor simulator 1 at the connectionpoint P1 through the connection line 6. That is, the reference potentialGND_B of the ECU 3 and the reference potential GND_A of the sensorsimulator 1 are connected to the ground in common. Meanwhile, theconnection line 6 corresponds to the “connection unit” of the invention.

According to the illustrative embodiment of the invention, the sensorsimulator 1 is adapted to have a circuit for processing a potential ofthe IN1 port and IN2 port of the input interface 20 different from thepotential of the CON port (i.e., the reference potential GND_A).Accordingly, the input interface 20 may obtain the potential of theOZ(−) port and the potential of the OZ(+) port of the reference sensor2, on the basis of (i.e., relative to) the reference potential GND_A. Inaddition, as described above, the input interface 7 of the ECU 3 is thesame as the input interface 20, and is adapted to have a circuit forprocessing a potential of the IN1 port and IN2 port of the inputinterface 7 different from the potential of the CON port (i.e., thereference potential GND_B). Since the ECU 3 and sensor simulator 1 areconnected to a common ground, the reference potential GND_A of thesensor simulator 1 and the reference potential GND_B of the ECU 3 mayslightly be different from each other due to a difference in, forinstance, wire resistance, but are nearly equal to each other.Accordingly, in both the case where the input interface 7 of the ECU 3is connected to the reference sensor 2 and the case where the inputinterface 20 of the sensor simulator 1 is connected to the referencesensor 2, the potential of the OZ(−) port may be maintained in a nearlyequal state, and the signal value of the detection signal, which isacquired by the sensor simulator 1, may equal the signal value of thedetection signal, which is acquired by the ECU 3.

According to the illustrative embodiment of the invention, the inputinterface 20 may obtain the potential of the OZ(−) port and OZ(+) portof the reference sensor 2, and output each of the potentials to themicrocomputer 10 through the A/D converter 30. The microcomputer 10 doesnot process the potential of the OZ(+) port, but rather the potentialdifference between the OZ(−) port and OZ(+) port by performing aprocessing program, as described below. Therefore, even in the casewhere the reference potential GND_A of the sensor simulator 1 changes,the potential difference between the OZ(−) port and OZ(+) port is notaffected. Thereby, the signal value of the detection signal may beprocessed with a high degree of accuracy.

The output circuit 40 may acquire the potential of the IN1 port of theinput interface 7 of the ECU 3 from the REF port, and superpose thepotential difference between the OZ(−) port and the OZ(+) port afterprocessing onto the potential of the IN1 port, to thereby output to theIN2 port of the input interface 7 through the OUT port. As describedabove, because a common ground is used, the potential of the IN1 port ofthe input interface 7 setting up the reference potential GND_B as astandard may specifically be predetermined even though the referencepotential GND_A is set up as a standard. Accordingly, even though someinconsistency between the reference potential GND_A and the referencepotential GND_B may develop due to a difference in wire resistance, thesignal value of the deterioration signal acquired by the ECU 3 does notdepend on the reference potential GND_A. This is because the potentialof the IN1 port based on the reference potential GND_B of the ECU 3 isset as a reference, and thereby is not affected by the inconsistency andhas a high degree of accuracy.

In addition, as described above, in the case where noise or potentialoffset occurs in the reference potential GND_B of the ECU 3, thereference potential GND_B may vary due to the noise or offset if thereference potential GND_A of the sensor simulator 1 is set as areference. However, the ECU 3 is driven on the basis of the referencepotential GND_B as a reference. In the case where the potential of theIN1 port based on the reference potential GND_B of the ECU 3 is affectedby noise or offset and changes accordingly, the signal value of thedetection signal, which is superposed (added) onto the potential of theIN1 port and inputted to the IN2 port, also changes equally. In thismanner, the potential difference between the N1 port and IN2 port is notaffected, and the degree of accuracy is high.

Next, the deterioration signal generation processes will be described.The deterioration signal is generated by processing the signal value(potential difference of the OZ(−) port and OZ(+) port) of the detectionsignal of the reference sensor 2 during the process of carrying out aprocessing program in the microcomputer 10 and superposing it onto thepotential of the IN1 port of the ECU 3 in the output circuit 40. Theprocessing program may perform any of a gain process, an offset process,a response delay process and a lag time delay process for the signalvalue of the detection signal. The detailed process methods of gainprocess, offset process, response delay process and lag time delayprocess are conventionally known and will be described brieflyhereinafter. For the details of the gain process, response delay processand waste time delay process, reference may be made to JP PatentPublication No. 2007-315210-A, for instance, incorporated herein byreference. In addition, for details of the offset process, reference maybe made to JP Patent Publication No. 2008-203152-A, incorporated hereinby reference. Meanwhile, the gain process, offset process, responsedelay process and lag time delay process correspond to the “gainoperation”, “offset operation”, “response characteristics operation” and“timing characteristics operation” of the invention, respectively.

The process for the signal value of the detection signal may beperformed at predetermined timing intervals (e.g., every 1 msec)according to the processing program that is executed in themicrocomputer 10. As shown in FIG. 3, the CPU 11 of the microcomputer 10may read the voltage (voltage value) of the OZ(−) port and OZ(+) port ofthe reference sensor 2, which is inputted to from the input interface 20through the A/D converter 30, thereby calculating a differential value.The differential value as calculated is stored in the RAM 13 as avariable Vdif (S11). In the step S11, the CPU 11, which performs anoperation on the differential value (first differential value) in thevoltage of the OZ(−) port and OZ(+) port of the reference sensor 2,corresponds to “operation unit” of the invention.

A gain processing (Vdif←Vdif×Gain), in which variable Vdif is multipliedby a predetermined gain factor Gain and the operational result issuperposed onto the variable Vdif, is executed (S13). The gainprocessing is a process for multiplying the signal value of detectionsignal by a gain factor Gain, thereby amplifying or attenuating thevalue. For example, as shown in FIG. 4, if the gain processing (herein,attenuation) is executed for an original (reference) detection signal asshown in FIG. 4(A), the detection signal may be processed as a detectionsignal whose signal value is increased or decreased (herein, decreased),in response to the gain factor Gain, as shown in FIG. 4(B).

Next, regarding the variable Vdif, an offset processing(Vdif←Vdif+Offset), in which variable Vdif is superposed onto apredetermined voltage value Offset and the operational result isoverwritten on the variable Vdif, is executed (S15). The offsetprocessing is a process for changing the signal value of detectionsignal by a predetermined voltage value Offset. As shown in FIG. 4, forexample, if the offset processing (herein, superposition of a plusvoltage value Offset) is executed for an original (reference) detectionsignal as shown in FIG. 4(A), the signal value may be processed as adetection signal whose signal value is changed up or down (herein,changed upwardly), as shown in FIG. (C).

Next, regarding the variable Vdif, a response delay process(Vdif←Vdif×1/(1+τs), in which an annealing is executed by performing anoperation applying, for instance, a first delay transfer function andthe operational result is rewritten on the variable, is executed (S17).The response delay process is a process for slowly changing (annealing)the signal value of detection signal. The first delay transfer functionG(s) is as follows.G(S)=k/(1−τs), wherein τ: time constant, k: gain (wherein provisionallypredetermined as k=1)

For example, as shown in FIG. 4, if the response delay process isexecuted for an original (reference) detection signal as shown in FIG.4(A), the signal value is slowly changed as compared with the originaldetection signal, thereby obtaining a detection signal delayed more thanand following the original detection signal, as shown in FIG. 4(D).

In addition, the lag time delay process is executed as to the variableVdif. The lag time delay process is a process for outputting a detectionsignal after time T that has been set up as a lag time. For example, asshown in FIG. 4, if the lag time delay process is executed for theoriginal detection signal as shown in FIG. 4(A), a detection signaldelayed in timing as compared with the original detection signal may beproduced, as shown in FIG. 4(E).

The lag time delay process, as described above, serves to subsequentlyadd an elapsed time information (first time, the elapsed time=0) to thecurrent variable Vdif, which has been processed by the gain process,offset process and response delay process (S19), as stored in the RAM 13(S21). Next, the elapsed time in all of the variables Vdif as storedprogresses by a unit time (S23). Also, the variable Vdif whose elapsedtime maintained as an elapsed time information reaches the waste time Tis outputted as a signal value of the detection signal after processingto the output circuit (40) through the D/A converter 50 (S25).Meanwhile, the variable Vdif as obtained at this time and stored in theRAM 13 in step S21 is maintained in the RAM 13 until the lag time Tlapses.

The processes in steps S11 to S25 each are performed with reference tothe signal value of detection signal, thereafter waiting a lapse ofpredetermined time of a period (e.g., 1 msec) (S27: NO) and thenreturning to step S11 (S27: YES) to thereby perform processing of thesignal value of detection signal as previously obtained. Meanwhile, theCPU 11, which performs operations on the signal value of the detectionsignal as processed in each of the steps S13 to S25, corresponds to the“processing means” of the invention.

Second Illustrative Embodiment

Next, the deterioration signal generation device of an oxygen sensoraccording to a second illustrative embodiment will be described withreference to FIG. 5. According to the second illustrative embodiment ofthe invention, the electric power source of the sensor simulator 1employs the same battery 4 as that of the ECU 3. As shown in FIG. 5, anoutput line (dotted line) of the battery 4 is connected to the BATterminal of the sensor simulator 1, and likewise the ground line of thebattery 4 is divided at the connection point P1 and connected to thereference potential GND_A of the sensor simulator 1 through the S_GNDterminal. The reference sensor 2, ECU 3, and sensor simulator 1 areidentical in configuration to those of the first illustrativeembodiment. The reference potential GND_B of the ECU 3 and the referencepotential GND_A of the sensor simulator 1 all are connected to theground line of the battery 4, thereby realizing a common ground. Thatis, if the sensor simulator 1 is supplied with electric power from thebattery 4, a common ground among the sensor simulator 1 and the ECU 3 iseasily realized. The sensor simulator 1 is also operated in the samemanner as in the first illustrative embodiment.

The invention is not limited to the illustrative embodiments describedabove, and various changes may be made within the spirit and scope ofthe claims appended hereto. For example, the output circuit 40 isconfigured by employing an instrumentation amplifier 41. However, theinstrumentation amplifier need not be incorporated into the electriccircuit. Instead, the electric circuit may be configured to superpose(add) a signal value of the detection signal as processed onto areference potential of the ECU 3 by employing an amplifier.

In addition, as described above, the processing program was executed inthe order of a gain process, an offset process, a response delay processand a lag time delay process. Alternatively, each of these processes maybe executed independently, and any of the processes need not beexecuted. That is, one or more than one of these processes may beexecuted. In addition, the order of the processes may be changedarbitrarily. In the case where the degree in gain of the detectionsignal or response delay and lag time are changed, if each of the gainfactor Gain for changing the gain, time constant τ of transfer functionG(s) and lag time T may independently be set in the case of a change inthe target air-fuel ratio from the rich side to the lean side or fromthe lean side to rich side, the sensor simulator 1 is preferablyemployed for developing a system capable of realizing an accurateair-fuel ratio feedback control.

In the present embodiment, the signal value of the detection signal isprocessed with software by performing the processing program, but it ispossible to process the signal value with an analog or digital circuithaving a logic circuit therein. In addition, an input/output interfacesuch as a USB or RS232C may be provided and connected to a personalcomputer by employing a corresponding cable, to allow for input of setvalues or checking on a display, etc. In addition, the detection signalof the reference sensor 2 or the deterioration signal as generated maybe output to a personal computer through an input/output interface suchas a USB or RS232C to produce output waveforms on the personal computerthat may be monitored. The output waveforms may also be displayed on thedisplay unit 80. In addition, the invention is not limited to the oxygensensor (reference sensor) 2 connected to the sensor simulator 1, havingan output value sharply which abruptly changes just above or below atheoretical air-fuel ratio, but may be applied to a sensor in which anappropriate catalyst layer is formed on a measuring electrode (electrodeexposed to an exhaust gas) provided in a solid electrolyte, and anoutput value which abruptly (sharply) changes just above or below anair-fuel ratio that has been shifted from a theoretical air-fuel ratioto a rich side or lean side by a predetermined value.

This application claims priority from Japanese Patent Application No.2010-010429, filed on Jan. 20, 2010, the disclosure of which isincorporated herein by reference in its entirety.

What is claimed is:
 1. A deterioration signal generation device forgenerating a deterioration signal simulating a deteriorated state of anoxygen sensor from a detection signal of the oxygen sensor, the oxygensensor outputting a detection signal which abruptly changes in signalvalue around a specific air-fuel ratio in response to concentration ofoxygen in an exhaust gas of an internal combustion engine, thedeterioration signal generation device outputting the deteriorationsignal to an external device, the deterioration signal generation devicebeing supplied with electric power from a power supply commonlyconnected to the external device, the deterioration signal generationdevice comprising: an interface which electrically connects thedeterioration signal generation device to a first output line at areference potential side of the oxygen sensor and to a second outputline at a sensor potential side of the oxygen sensor that changes inpotential in response to oxygen concentration, and that acquires a firstpotential of the first output line and a second potential of the secondoutput line; a calculator configured to calculate a first differentialvalue between the first potential and the second potential; a processorconfigured to perform one or more operations on the first differentialvalue in response to a target deterioration state to thereby obtain asecond differential value; an operational amplifier configured toacquire a third potential of a first input line at a reference potentialside of the external device, wherein the first input line is connectedto the first output line in a case where the oxygen sensor is connectedto the external device; and an output circuit configured to generate thedeterioration signal having as a signal value a fourth potentialobtained by superposing the second differential value on the thirdpotential, to thereby output the deterioration signal to a second inputline at a sensor potential side of the external device, wherein thesecond input line is connected to the second output line in a case wherethe oxygen sensor is connected to the external device.
 2. Thedeterioration signal generation device according to claim 1, wherein theprocessor is configured to perform at least one operation that simulatesa predetermined deterioration state selected from the group consistingof: a gain operation for changing a gain of signal value of thedetection signal; an offset operation for changing a signal value of thedetection signal up or down by a fixed amount; a timing characteristicsoperation for delaying response of the detection signal to a change inconcentration of a specific component in a target gas to be measured;and a response characteristics operation for changing a rate of changeof the detection signal in response to a change in concentration of aspecific component in a target gas to be measured, to thereby processthe first differential value into the second differential value.